Complex formation equilibria in iron(III)-L-alanine system

Summary Complex formation in iron(III)-L-alanine solutions was studied by emf glass electrode and spectrophotometric measurements, in 0.5 mol dm ^–3 (Na)NO₃ medium, at 25 ° C. In the concentration range 0.5 [Fe]₀ 20.0, 5.0 [Ala]₀ 1000.0 (mmol dm^–3) and 1.0 -log [H⁺] 3.5; {[Ala]/[Fe] = 10:1-100:1| the equilibria in the title system were explained by the model including the species FeHL, FeL, Fe(OH)L, Fe₂(OH)₂L₂ (where HL denotes L-alanine) and several hydrolytic products. The stability constants of complexes are given. The mechanism of formation and structure of complexes in solution is proposed.Abbreviations Ala alaninate ion - HAla alanine (zwitterion) - AlaH alanine (neutral) - H₂Ala⁺ alanine cation     

29Si-MAS-NMR-Untersuchungen an binären Kaliumsilicatgläsern Ein Beitrag zur Interpretationskontroverse

High-resolution solid-state²⁹Si-MAS-NMR spectra of binary potassium silicate glassesnK₂O·SiO₂ (0n1) have been investigated. The qualitative interpretation suggests the validity of theQ ⁿ /Q ^n–1 concept without statistical distribution of the differentQ ⁿ units.

     

Bis(η5-cyclopentadienyl)-brenzkatechinato-titan(IV) — ein oligomerer Mehrkernkomplex

Cp ₂TiCl₂ reacts with 1,2-(LiO)₂C₆H₄ producing the pyrocatecholato complex [Cp ₂Ti(O₂C₆H₄-o)] _n . Osmometric molecular weight determination, temperature-variable¹H NMR, and MS indicate an oligomeric polynuclear complex (2n4). Its MS fragmentation behaviour is observed by metastable transitions.

     

2,3-Dihydroxypyridine Loaded Amberlite XAD-2 (AXAD-2-DHP): Preparation, Sorption–Desorption Equilibria with Metal Ions, and Applications in Quantitative Metal Ion Enrichment from Water, Milk and Vitamin Samples

2,3-Dihydroxypyridine loaded (via –N=N–linker) Amberlite XAD-2 (AXAD-2-DHP) was prepared and characterized by elemental analyses, TGA and FT-IR spectra. It (1g packed in a column of 1cm diameter; surface area 135.5m²g^–1) was found to be an effective solid phase sorbent for enriching Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺ at pH 3.5 to 7.0 using flow rates between 1.0–5.0mLmin^–1. For desorption (recovery 97.0–99.8%) of the metal ions, 8 to 10mL of 2.0molL^–1 HCl or 1.5molL^–1 HNO₃ at a flow rate of between 2.0 and 4.0mLmin^–1 were found most suitable. The t_1/2 (time for 50% sorption) is between 2 and 10min when a 50mL solution (containing a total amount of metal of 2mg) was equilibrated with 0.5g of resin. Sorption of all metal ions except Pb²⁺ follows the Langmuir model, whereas for Pb the data fits with the Freundlich model. The sorption capacity is between 60.7 (for Cd) and 406.7 (for Cu) µmolg^–1. The resin can withstand an acid concentration of 6molL^–1 and can be reused for thirty cycles of sorption–desorption. The preconcentration factor varies between 100 and 300. For Cd, Ni and Cu the sorption capacity of 2,3-dihydroxypyridine loaded cellulose is lower than that of the present resin. The tolerance limits of electrolytes, humic acid, complexing agents, Ca²⁺ and Mg²⁺ in the enrichment of all metal ions are reported. The limits of detection are 3.88, 5.37, 8.72, 13.88, 4.71, 1.24, 0.59 and 0.30µgL^–1 for Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺, respectively. The calibration curves for flame AAS determination were linear in the ranges 0.018–1.0, 0.067–5.0, 0.2–5.0, 0.9–20, 0.028–2.0, 0.077–5.0, 0.19–10 and 0.1–3.5µgmL^–1, respectively. All the eight metal ions in river and synthetic water samples, Co in vitamin tablets and Zn in milk samples have been quantitatively enriched with Amberlite XAD-2-DHP and determined by flame atomic absorption spectrometry.     

The electronic structure and spectrum of the silver(I)perchlorate-pyridine complex

The absorption spectrum of the silver perchlorate-pyridine system was measured in acetonitrile and ethanol in the wavelength region of 180 m to 400 m. It was found that the solution exhibits a new shoulder in the 210 m region characteristic for the 11 complex, in addition to the absorption maxima at 196 m and 253 m which correspond, respectively, to the L _a and L _b bands of pyridine. From the concentration dependence of the absorption intensity of this shoulder, the equilibrium constant for 11 complex formation was determined to be 108 l/mole at 26 °C. Furthermore, we studied theoretically the electronic structure of this complex by the method of the localized orbital model, the effect of the solvation energy upon the charge-transfer configurations being taken into account. The theoretical results show that the new absorption band at 207.5 m has to considerably great extent the character of a charge-transfer type excitation.

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Zusammenfassung Das Absorptionsspektrum des Systems AgClO₄-Pyridin in Acetonitril- und Äthanol-Lösung wurde im Bereich von 400-180 m vermessen. Es treten Absorptionsmaxima bei 196 und 253 m auf, die der L _a -bzw. L _b -Bande des Pyridins entsprechen; daneben eine Schulter bei 207 m als Charakteristikum des 11-Ag⁺-Pyridin-Komplexes. Aus der Konzentrationsabhängigkeit der Intensität dieser Schulter folgt als Gleichgewichtskonstante der Komplexbildung k=108 l/Mol (26 °C), aus der Temperaturabhängigkeit H=4,5 kcal/Mol, S=–6 Cl in guter Übereinstimmung mit polarographischen Ergebnissen. Weiterhin wurde die Elektronenstruktur mit der Methode der Moleküle in Molekülen unter Berücksichtigung von Solvatationseinflüssen untersucht. Danach ist die neue Schulter als Ladungsübergangsbande zu klassifizieren.

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Résumé Mesure du spectre d'absorption du système AgClO₄-Pyridine en milieu acétonitrile ou éthanol dans le domaine 400-180 m. On obtient des maxima d'absorption vers 196 et 253 m correspondant aux bandes L _a et L _b de la pyridine; un épaulement vers 207 m est caractéristique du complexe 11-Ag⁺-Pyridine. D'après la variation de l'intensité de cet épaulement avec la concentration on obtient comme constante d'équilibre du complexe k=100 l/Mol (26 °C), et à partir de la variation avec le température H=4,5 kCal/Mol, S=–6 Cl, en bon accord avec les résultats polarographiques. De plus la structure électronique est étudée à l'aide de la méthode des molécules dans les molécules en considérant les effets de solvatation. On en déduit le caractère de bande de transfert de charge de cet épaulement.

     

Mechanism of the voltammetric reduction of phenolphthalein at the mercury electrode inDMF

The electrochemical reduction of phenolphthalein in dimethylformamide solution containing 0.1 mol dm^–3 tetraethylammonium perchlorate at the hanging dropping mercury electrode showed an irreversible two-electron voltammetric peak. It was found that the CV peak is diffusion-controlled at low concentrations (0.4 mmol dm^–3). At higher concentration (0.5 mmol dm^–3) a postpeak was developed besides the diffusion-controlled one which was assigned to the adsorbed depolarizer. Cyclic voltammetric studies indicate that phenolphthalein follows an ECEC mechanism. Convolution and deconvolution potential sweep voltammetry confirm that mechanism.

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Mechanismus der voltametrischen Reduktion von Phenolphthalein an der Quecksilberelektrode inDMF

Zusammenfassung Die elektrochemische Reduktion von Phenolphthalein an der tropfenden Quecksilberelektrode in Dimethylformamidlösung mit einem Gehalt von 0.1 mol dm^–3 an Tetraethylammoniumperchlorat zeigte ein irreversibles voltametrisches Maximum für zwei Elektronen. Es zeigte sich, daß der CV-Peak bei niederen Konzentrationen (0.4 mmol dm^–3) diffusionskontrolliert ist. Bei höheren Konzentrationen (0.5 mmol dm^–3) entwickelte sich ein nachkommendes Maximum neben dem diffusionskontrollierten, welches dem adsorbierten Depolarisator zugeordnet wurde. Untersuchungen mittels cyclischer Voltametrie zeigten, daß Phenolphthalein einem ECEC-Mechanismus folgt. Konvolutions-und Dekonvolutions-Potential-Sweep-Voltametrie bestätigten diesen Mechanismus.

     

Spectrophotometric determination of plutonium with chlorophosphonazo III

Summary Plutonium(IV) forms a Chlorophosphonazo III complex in 0.5–2M hydrochloric acid. Maximum absorbance occurs at 620 and 685 nm. Beer's law is obeyed over the range of 0–50g per 10 ml and the molar absorptivity is 3.7×10⁴ mol^–1 cm^–1 at 690 nm. Plutonium can be determined in the presence of fluoride, sulfate and phosphate. However, lanthanides, thorium, uranium and zirconium interfere seriously.

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Zusammenfassung Plutonium(IV) bildet in 0,5-bis 2-m Salzsäure mit Chlorphosphonazo III eine Komplexverbindung, deren Absorptionsmaxima bei 630 und 685 nm liegen. Bis 50 g/10 ml entspricht die Farbe dem Beer'schen Gesetz; die molare Extinktion bei 690 nm beträgt 3,7·10⁴l·Mol^–1·cm^–1. Plutonium kann damit in Gegenwart von F^–, SO₄ ^2– und PO₄ ^3– bestimmt werden. Lanthanide, Th, U und Zr stören jedoch ernstlich.

     

Gamma radiolysis of Methyl Red solution and reaction induced by γ-irradiated NaCl in Methyl Red

The -radiolysis of Methyl Red solution in HCl medium at pH=2 has been studied along with energy transfer reaction brought about byF and hole centers of -irradiated NaCl. The G-values for degradation of the azo dye indicator by radiolysis and -irradiated salt were determined as 9·10^–1 and 4.8·10^–3, respectively. The kinetic rate constants (k) of degradation are evaluated as 2·10^–5 rad^–1 in the case of direct radiolysis, while for the irradiated salt it is 2·10^–7 rad^–1. The extent of degradation by direct -radiolysis is 100–200 times greater as compared to that by the -irradiated salt. The same mechanism is proposed for radiolysis as well as the reaction induced by -irradiated sodium chloride.     

The kinetics of base hydrolysis of [Co(trien)(amine)Cl]2+ complexes (amine=imidazole,pyridine,n-butylamine and 2,2-dimethoxyethylamine)

Summary The complexescis--[Co(trien)(ImH)Cl]²⁺ (ImH=imidazole, trien=1,8-diamino-3,6-diazaoctane),cis--[Co(trien)(Buⁿ-NH₂)Cl^–]²⁺,cis--[Co(trien)(NH₂CH₂-CH(OMe)₂)Cl^–]²⁺ andcis-₂-[Co(trien)(py)Cl]²⁺ (py=pyridine) have been characterised and their kinetics of base hydrolysis studied. Thecis--isomers which have afac-fac arrangement of the trien ligand have values of k _OH ²⁵ in the 73 to 253 dm³ mol^–1 s^–1 range at I=0.1 mol dm^–3. Extremely rapid base hydrolysis is observed withcis-₂-[Co(trien)(py)Cl]²⁺ where k _OH ²⁵ is 6.65×10⁶ mol³ mol^–1 s^–1 at I=0.1 mol dm^–3. This complex has amer-fac arrangement of the trien ligand with flatsec-NH donor leading to rapid base hydrolysis due to good -overlap between the conjugate base and cobalt(III). The pyridine ligand causes aca. 30 fold rate increase compared with the hydrolysis ofcis-₂-[Co(trien)(NH₃)Cl]²⁺.     

Untersuchungen über die diamagnetische Suszeptibilität einiger Organo (imino-oxy)silane

Diamagnetic susceptibilities of trimethyl(imino-oxy)silanes,Me ₃SiON CMeR, and dimethyldi(imino-oxy)silanes,Me ₂Si(ON CMeR)₂, containing Si–O bonds are reported. _M of these silicon compounds has been calculated theoretically from the method ofBaudet et al. and a good agreement has been obtained between the observed _M values and the corresponding calculated values. _Si in these compounds has been calculated graphically and the lower values have been explained on the basis of back-bonding to the silicon atom from the oxygen lone pair.